Method and arrangement in a wireless communication system

ABSTRACT

The present invention relates to a method and arrangement in base station for scheduling user equipments. The base station is adapted to schedule communication from user equipments by sending contention based grants comprising information indicating if the contention based grant should be used for initial transmission or for retransmission. If it is detected that data is not correctly received due to a collision, the information in a following contention based grant is set to indicate that said contention based grant is to be used for initial transmission, while if data is not correctly received, but no collision is detected, the information is set to indicate that the contention based grant is to be used for retransmission. Corresponding method and arrangement in a user equipment is described.

TECHNICAL FIELD

The present invention relates to a method and an arrangement in a basestation and a method and an arrangement in a user equipment. Inparticular, it relates to a mechanism for scheduling user equipmentswithin a wireless communication system adapted for contention basedtransmissions.

BACKGROUND

Hybrid Automatic Repeat reQuest (HARQ) with soft combining is aneffective way to correct transmission errors in systems involvingwireless transmission. HARQ is a variation of standard Automatic RepeatreQuest (ARQ), where an error detection code is used to detecttransmission errors, and in the case errors are detected, the packet isrequested for retransmission.

The basic idea of HARQ, for uplink transmission, is that after receivingdata in an uplink subframe the base station, in LTE referred to asevolved NodeB (eNodeB or eNB), attempts to decode the data and thenreports to the user equipment whether the decoding was successful bysending an acknowledgement (ACK) or unsuccessful by sending a negativeacknowledgement (NACK). In the case of an unsuccessful decoding attempt,the user equipment thus receives a NACK in a later downlink subframe,and can retransmit the data that was not successfully received at theeNB.

HARQ with soft combining, sometimes referred to as Type II HARQ, usesForward Error Correction to correct transmission errors from successive(re-)transmissions. The receiver stores soft copies of each failedtransmission attempt. By combining the soft copies of each transmissionattempt, the receiver has an increasing probability of correct decodingof the original packet. With type II HARQ, the receiver is thus able touse the cumulative energy of each transmission attempt. With plain ARQ,each retransmission attempt is decoded standalone, and thus does nothave this gain.

Contention based uplink transmissions is a new technique that is beingdiscussed in 3rd Generation Partnership Project (3GPP) for the Release10 version of Long Term Evolution (LTE). The purpose is to reduce accessdelay and signalling overhead by letting user equipments transmit dataon contention based (CB) grants. Contention based grants are signalledon Physical Downlink Control Channel (PDCCH) in the same way asdedicated uplink grants, but the grants are addressed to a group ofusers. User equipments can use the contention based grants to transmitdata without prior transmission of Scheduling Request. Thus, the accesstime is reduced. Contention Based transmission may be feasible for usersthat have uplink synchronization. Contention based grants are addressedto Contention based Radio Network Temporary Identifiers, RNTIs,(CB-RNTIs). However, since many user equipments can use the samecontention based grant, it is difficult to use the Hybrid AutomaticResend reQuest (HARQ) protocol to correct transmission errors, sincetypically errors are caused by interference from other user equipmentsending data at the same time.

In the case of a decoding error in a contention based transmissionscheme, the eNB will not be able to determine the identity of thetransmitting user equipment. The eNB will therefore not be able tocorrectly combine (re-)transmissions from different user equipmentstransmitting of the same grant. Thus, the HARQ operation is not feasibleto correct transmission errors caused by collision. Given the fixedretransmission timing used in e.g. High Speed Packet Access (HSPA) andLTE, retransmissions would only cause a new collision. However, whenthere is no collision, i.e. only one UE is transmitting, HARQ caneffectively be used to correct transmission error, in the same way as itis used for dedicated grants.

Yet, having a retransmission scheme would significantly improve theperformance in the cases where the transmissions are not successful.

In addition, a missed assignment will in general result in block errorsthat need to be corrected by higher-layer protocols, which in turn has anegative impact on performance in terms of throughput and latency. Also,increasing the delay may cause undesirable interactions withTransmission Control Protocol (TCP) based applications.

SUMMARY

It is therefore an object of the present invention to provide amechanism for improving the performance in a wireless communicationsystem.

According to a first aspect of the present invention, the object isachieved by a method in a base station for scheduling user equipments ina cell. The base station and the user equipments are comprised in awireless communication system adapted for contention basedtransmissions. The base station is adapted to schedule the communicationfrom the user equipments by sending contention based grants. The methodcomprises sending a contention based grant of a retransmission processto a plurality of user equipments within the cell, receiving data fromat least one user equipment using said contention based grant andverifying if data is correctly received from at least one userequipment. If it is verified that data is not correctly received, themethod comprises sending a non-acknowledgement feedback “NACK” to theplurality of user equipments. The method furthermore comprises detectingif data is not correctly received due to a collision, and sending afollowing, or second contention based grant belonging to the sameretransmission process as the first contention based grant, to theplurality of user equipments. A contention based grant according toembodiments of the invention comprises information indicating if thecontention based grant should be used for initial transmission or forretransmission. If it is detected that data is not correctly receiveddue to a collision, the information in the following contention basedgrant is set to indicate that said contention based grant is to be usedfor initial transmission. If data is not correctly received, but nocollision is detected, the information in the following contention basedgrant is set to indicate that said contention based grant is to be usedfor retransmission, such as Hybrid Automatic Repeat Request HARQretransmission.

Hereby, if it is detected that data is not correctly received due to acollision, the information in the next contention based grant is set toindicate that said contention based grant is to be used for initialtransmission. Otherwise, if data is not correctly received, but nocollision is detected, the information in said contention based grant isset to indicate that the second contention based grant is to be used forretransmission, such as e.g. a Hybrid Automatic Repeat Request HARQretransmission.

According to a first embodiment of the first aspect, the informationindicating if the contention based grant should be used for initialtransmission or for retransmission is provided as a state bit indicatorwhere a first value indicates that the contention based grant should beused for initial transmission and a second value indicates that thecontention based grant should be used for retransmission. Said state bitindicator is in a specific embodiment a New Data Indicator, NDI.

According to an alternative embodiment, the information indicating ifthe contention based grant should be used for initial transmission orfor retransmission is provided as an identifier used to address theplurality of user equipments. Said identifier may be a ContentionBased—Radio Network Temporary Identifier “CB-RNTI”, wherein differentCB-RNTIs are used for indicating if the contention based grant should beused for initial transmission or for retransmission.

According to a second aspect of the present invention, the object isachieved by an arrangement in a base station for scheduling userequipments in a cell. The base station and the user equipments arecomprised in a wireless communication system adapted for contentionbased transmissions. The base station is adapted to schedule thecommunication from the user equipments by sending contention basedgrants. The arrangement comprises a transmitter, adapted to sendcontention based grants and to send feedback to a plurality of userequipments within the cell. The arrangement furthermore comprises areceiver, adapted to receive data from at least one user equipment and averification unit adapted to verify if data is correctly received fromat least one user equipment. The arrangement furthermore comprises adetecting unit adapted to detect if data is not correctly received dueto a collision. The arrangement furthermore comprises a determinationunit adapted to generate feedback and set information comprised in afollowing, or second contention based grant. If data is not correctlyreceived, and a collision is detected, the information in the following,or second, contention based grant is set to indicate that saidcontention based grant is to be used for initial transmission. If datais not correctly received, but no collision is detected, the informationin the following, or second, contention based grant is set to indicatethat said contention based grant is to be used for retransmission.

According to a third aspect of the present invention, the object isachieved by a method in a user equipment for assisting a base station inscheduling user equipments in a cell. The base station and the userequipments are comprised in a wireless communication system adapted forcontention based transmissions and the user equipment is adapted toreceive contention based grants from the base station. The methodcomprising receiving a contention based grant from the base station,wherein the contention based grant comprises information indicating ifthe contention based grant should be used for initial transmission orretransmission. The method further comprises detecting the informationcomprised in said contention based grant, and sending data to the basestation using said contention based grant, in accordance with theindication of the information comprised in the contention based grant.

Thus, the information comprised in the received contention based grantindicates if the contention based grant should be used for initialtransmission or for retransmission. The data to be sent to the basestation is initial transmission data or retransmission data, dependingon the detected information comprised in the received contention basedgrant.

According to a first embodiment of the second aspect, the informationindicating if the contention based grant should be used for initialtransmission or for retransmission is provided as a state bit indicatorwhere a first value indicates that the contention based grant should beused for initial transmission and a second value indicates that thecontention based grant should be used for retransmission. Said state bitindicator is in a specific embodiment a New Data Indicator, NDI.

According to an alternative embodiment, the information indicating ifthe contention based grant should be used for initial transmission orfor retransmission is provided as an identifier used to address theplurality of user equipments. Said identifier may be a ContentionBased-Radio Network Temporary Identifier “CB-RNTI”, wherein differentCB-RNTIs are used for indicating if the contention based grant should beused for initial transmission or for retransmission

According to a specific embodiment, if a non-acknowledgement feedback,NACK, is received and the information comprised in the following grantof the same retransmission process as the first grant indicates that thegrant should be used for initial transmission, then the method comprisestriggering a radio link control, RLC, retransmission. A specificembodiment comprises adding a random delay before the radio link controlretransmission of data is performed.

According to yet another embodiment, if a NACK is received and theinformation comprised in the following contention based grant of thesame retransmission process as the first contention based grantindicates that the grant should be used for retransmission, aretransmission of data, such as Hybrid Automatic Repeat Request “HARQ”retransmission should be performed.

According to yet another embodiment, the method comprises, if a NACK isreceived, activating a sending prohibit timer, which sending prohibittimer prevents the user equipment from using any grants received fromthe base station before the sending prohibit timer has timed out. Thesending prohibit timer may be arranged to be deactivated when a dynamicgrant, dedicated to the user equipment, is received.

According to a fourth aspect of the present invention, the object isachieved by an arrangement in a user equipment for assisting a basestation in scheduling user equipments in a cell. The base station andthe user equipments are comprised in a wireless communication systemadapted for contention based transmissions. The user equipment isadapted to receive contention based grants from the base station. Thearrangement comprises a receiver adapted to receive a contention basedgrant comprising information indicating if the contention based grantshould be used for initial transmission or for retransmission and adetecting unit, adapted to detect said information. The arrangementfurthermore comprises a transmitter, adapted to transmit data to thebase station using said contention based grant, in accordance with theindication of the information comprised with the contention based grant.

Embodiments of the present methods and arrangements further improve thecontention based concept. According to embodiments of the presentmethods and arrangements, the identity of the user equipment sendingdata does not need to be transmitted to the base station, which savesresources. Further, the overall reduced signalling resulting from thepresent methods and arrangements render higher capacity and bettercoverage within the wireless communication system. Thus the performanceof the wireless communication system is improved.

An advantage of embodiments of the present methods and arrangements isthat HARQ operation is supported for contention based transmission.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail with reference to attacheddrawings illustrating exemplary embodiments of the invention and inwhich:

FIG. 1 is a schematic block diagram illustrating embodiments of awireless communication system.

FIG. 2 is a combined signalling and flowchart illustrating radio signaltransmission according to some embodiments.

FIG. 3 a is an illustration depicting an operation with successful radiosignal transmission, according to some embodiments.

FIG. 3 b is an illustration depicting unsuccessful radio signaltransmission, according to some embodiments, due to collision.

FIG. 3 c is an illustration depicting unsuccessful radio signaltransmission, according to some embodiments, but no collision isdetected.

FIG. 4 is a flow chart illustrating embodiments of a method in a basestation.

FIG. 5 is a schematic block diagram illustrating embodiments of a basestation arrangement.

FIG. 6 is a flow chart illustrating embodiments of a method in a userequipment.

FIG. 7 is a schematic block diagram illustrating embodiments of a userequipment arrangement.

DETAILED DESCRIPTION

The invention is defined as a method and an arrangement in a basestation and a method and an arrangement in a user equipment, which maybe put into practice in the embodiments described below. This inventionmay, however, be embodied in many different forms and is not to beconsidered as limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and convey the scope of the invention to those skilled in theart.

Still other objects and features of the present invention may becomeapparent from the following detailed description considered inconjunction with the accompanying drawings.

It is to be understood, however, that the drawings are designed solelyfor purposes of illustration and not as a definition of the limits ofthe invention, for which reference is to be made to the appended claims.It is further to be understood that the drawings are not drawn to scaleand that they are merely intended to conceptually illustrate thestructures and procedures described herein.

FIG. 1 depicts a wireless communication system 100, such as e.g. theE-UTRAN, LTE, LTE-Adv, 3rd Generation Partnership Project (3GPP) WCDMAsystem, Global System for Mobile communications/Enhanced Data rate forGSM Evolution (GSM/EDGE), Wideband Code Division Multiple Access(WCDMA), Worldwide Interoperability for Microwave Access (WiMax), orUltra Mobile Broadband (UMB), just to mention some possible options.

The wireless communication system 100 may comprise a base station 110, afirst user equipment 120 and a second user equipment 122 adapted tocommunicate with each other over at least one radio channel, within acell 130. The wireless communication system 100 is adapted for acontention based transmission scheme.

The base station 110 may be referred to as e.g. a NodeB, an evolved NodeB (eNode B, or eNB), a base transceiver station, Access Point BaseStation, base station router, or any other network unit capable tocommunicate with the user equipment 120, 122 within the cell 130,depending e.g. of the radio access technology and terminology used. Inthe rest of the description, the term “base station” will be used, inorder to facilitate the comprehension of the present methods andarrangements.

The user equipments 120, 122 may be represented by e.g. a wirelesscommunication terminal, a mobile cellular phone, a Personal DigitalAssistant (PDA), a wireless platform, a laptop, a computer or any otherkind of device capable to communicate wirelessly with the base station110. Further, the user equipments 120, 122 within the cell 130 may,according to some embodiments be grouped together in subsets of userequipments 120, 122, forming contention based groups.

In the following, the present methods and arrangements are furtherelaborated with specific reference to LTE systems and more particularlywith respect to the uplink in LTE, i.e. for the link from the userequipment 120, 122 towards the base station 110. However, it is obviousto a skilled person that corresponding concepts could also be applied inother wireless communication systems 100.

A basic concept of a contention based transmission scheme is that userequipments 120, 122 are allowed to use uplink resource blocks in acontention based fashion. According to some embodiments, uplinkresources that have not been allocated to any dedicated user equipment120, 122, and would thus otherwise be left unused, may be offered forcontention based grant. In this way, the resources for contention basedaccess do not affect other scheduled uplink transmissions according tothose embodiments.

A general property of contention based transmissions is that the errorrate may increase if data packets collide with each other. Collisionsreduce the transmission throughput and the throughput becomes sensitiveto the system load. If the load is allowed to increase beyond a certainlimit, the collision probability increases rapidly, the wirelesscommunication system 100 may become unstable, and the throughput maydecrease. Therefore, contention based transmissions may not interferewith dedicated transmissions, according to some embodiments. Thus, eachallocated resource block may either be allocated for contention basedtransmission or dedicated transmission. One way to achieve suchisolation is to allow contention based transmission only in uplinkresource blocks that have not been reserved for dedicated uplinktransmission.

Embodiments of the present methods and arrangements introduce adaptiveretransmission operation such as e.g. HARQ retransmission operation, tothe concept of contention based transmissions in LTE. The basicprinciple is to support HARQ retransmission when no collision isdetected, but to refrain from HARQ retransmission if a collision isdetected. Hereby, unwanted collisions of HARQ retransmissions can beavoided, while still using the HARQ gain to correct transmission errorsnot caused by collision. Thus, according to embodiments of theinvention, the base station 110 is able to enable/disable HARQretransmission at the user equipment 120, 122 dependent on if data wasnot correctly received due to a collision of data transmissions or not.If data was not correctly received due to a collision, a followingcontention based grant should only be used for initial transmission.Consequently, if data was not correctly received, but no collision hasoccurred, a following contention based grant should only be used forretransmission.

In a specific embodiment, the base station 110 may use a state bit suchas e.g. the New Data Indicator (NDI) in the contention based grant toindicate to the user equipment 120, 122 whether to use the contentionbased grant for retransmission or not. The state bit, e.g. the NDI, maybe set to a first value indicating that the contention based grant is tobe used for initial transmission, or to a second value, indicating thatthe contention based grant is to be used for retransmission, such ase.g. a Hybrid Automatic Repeat Request HARQ retransmission. The firstvalue may be 0 and the second value may be 1. However, according to sameembodiments, the first value may be 1 and the second value may be 0.Thus the base station 110 is able to enable/disable HARQ retransmissionat the user equipment 120, 122.

Alternatively, in another specific embodiment, whether or not to use thecontention based grant for retransmission can be indicated withdifferent CB-RNTIs for initial transmission and retransmission such thatthe base station 110 controls the HARQ operation by means of usingdifferent CB-RNTIs for indicating that the contention based grant is tobe used for initial transmission and retransmission, e.g. HARQretransmission, respectively. For example, providing an uplinkcontention based grant to a first CB-RNTI indicates that user equipment120, 122 may only use the contention based grant for initialtransmission. Providing an uplink grant to a second CB-RNTI indicatesthat the grant is only for retransmissions, i.e. only a user equipment120, 122 that performed a transmission on the same HARQ process one RTTbefore and received a NACK is allowed to use the contention based grantto transmit a HARQ retransmission. In this way, user equipment 120, 122wanting to initiate new transmission are blocked from using thiscontention based grant and the collision probability is decreased.

The present methods and arrangements may also make use of a Local NACKin the user equipment 120, 122. Thus upon receiving a NACK as a responseto the contention based transmission, and the next received contentionbased grant comprises information indicating that the contention basedgrant is only to be used for initial transmission, the user equipment120, 122 may perform a Local NACK from Medium Access Control (MAC) toRadio Link Control, RLC, to trigger an RLC retransmission. The idea isthus that the HARQ transmitter provides local NACK to the ARQtransmitter. The local NACK concept is known from e.g. Tdoc R2-060374.Furthermore, a random delay may optionally be added before the RLCtransmission in order to spread the RLC retransmissions in time to avoidfurther collisions, according to some embodiments.

The MAC is situated in the protocol sub-layer above the physical layerand below the RLC layer in the LTE protocol stack. The connection to thephysical layer below is through transport channels, and the connectionto the RLC layer above is through logical channels. The MAC layer mayperform data transmission scheduling and multiplexing/demultiplexingbetween logical channels and transport channels. In the user equipment120, 122, it may also be responsible for control of random access,timing advance and discontinuous reception.

The RLC layer is located between the Packet Data Convergence Protocol(PDCP) layer and the MAC layer in the LTE user plane protocol stack. Themain functions of the RLC layer are segmentation and reassembly of upperlayer packets in order to adapt them to the size which can actually betransmitted over the radio interface. For radio bearers which neederror-free transmission, the RLC layer also may perform retransmissionto recover from packet losses. Additionally, the RLC layer may performreordering to compensate for out-of-order reception due to HARQoperation in the MAC layer. There may be one RLC entity per radiobearer.

FIG. 2 is a combined signalling and flowchart illustrating radio signaltransmission according to some embodiments. The purpose of thisillustration is to provide a general overview of the present methods andthe functionalities involved.

The present methods and arrangements are related to a scenariocomprising at least one user equipments 120, 122 in the cell 130 withuplink time alignment but no scheduling grant is allocated. The userequipment 120, 122 may receive data in its buffer, and the presentmethods and arrangements relates to how to minimize the latency for thisdata to be securely transmitted to the base station 110 over the airinterface.

In a first step, the base station 110 schedules and sends a contentionbased grant to a plurality of user equipments 120, 122 within the cell130. The contention based grant may be sent to all user equipments 120,122 within the cell 130, or sent to a subset of user equipments 120, 122within the cell 130, i.e. subsets of user equipments 120, 122 formingcontention based groups, according to different embodiments. Thecontention based grant comprises information indicating if the grantshould be used for initial transmission or for retransmission. Theinformation may as previously explained be provided for example as astate bit that may be set, e.g. preset, to a first value or a secondvalue, according to some embodiments.

The plurality of user equipments 120, 122 may optionally form contentionbased groups, which may be given access to different contention basedresources. Thus for example, there may be a premium user contentionbased group and a regular user contention based group, just to mentionan arbitrary example.

Thus any synchronized user equipments 120, 122 with uplink data but novalid grant can now read a contention based grant and use it to make acontention based data transmission, either an initial transmission or aretransmission in accordance with the information comprised in thegrant.

When the base station 110 receives signalling from the user equipments120, 122, the base station 110 may perform some verification of thecorrectness of the received data. Thus the base station 110 may attemptto decode the transport blocks in the uplink sub-frames in which it hasdetected an assignment and for example by means of a Cyclic RedundancyCheck (CRC) estimate whether the transport block is correctly receivedor not.

If it is verified that data is correctly received from at least one ofthe user equipments 120, 122, then an acknowledgement ACK may begenerated. If data is not correctly received by at least one of the userequipments 120, a negative acknowledgement, or non-acknowledgement NACKis generated.

Also, if data is not correctly received, a detection is made in order tofind out if a collision of data transmissions has occurred. A collisionmay occur if two or more user equipments 120, 122 try to send signalssimultaneously over the same resource, e.g. the same channel.

Also information is set to indicate if the grant should be used forinitial transmission or for retransmission dependent on if a collisionwas detected. For example, if a collision is detected, a state bit, suchas e.g. NDI, of the next grant to be sent is set to a first value,indicating that the next contention based grant is only to be used forinitial transmission.

Else, if no collision has been detected, but data was still notcorrectly received, the information of the next grant to be sent is setto indicate that the next contention based grant is to be used forretransmission, such as e.g. a Hybrid Automatic Repeat Request HARQretransmission. For example, a state bit such as e.g. NDI, of the nextgrant to be sent is set to a second value.

Thus, the present methods and arrangements minimize, or at leastsomewhat reduce wasting radio resources on redundant retransmissions.

The feedback ACK/NACK may be sent on the PHICH channel. PHICH isdetermined from the Control Channel Element (CCE) of the PDCCH carryingthe contention based grant. However, in this case, all user equipments120, 122 that used the contention based grant may also read thecontention based feedback, ACK or NACK. Thus, the feedback according tothe present methods and arrangements has a one to many mapping, insteadof a one to one mapping that is usually assumed with HARQ feedbackaccording to some embodiments.

Since the feedback will possibly be received by a plurality of userequipment 120, 122, there may be rules on what feedback to send, in casethe feedback should in reality be different for different user equipment120, 122 according to some embodiments.

The user equipments 120, 122 receiving the ACK or NACK feedback evaluatethe feedback. If an ACK has been received, the user equipment 120, 122regard the transmission as successful, and continues sending the nextdata whenever the subsequent grant, which may be yet a contention basedgrant or a dedicated grant, is detected according to some embodiments.If a NACK is received, the information comprised in the next receivedgrant, for example a state bit, has to be further analysed. When nextcontention based grant is received from the base station 110, it isdetected if the information comprised in the received contention basedgrant is set to indicate an initial transmission or a retransmission.

Then data may be sent, or alternatively resent, to the base station suchthat initial transmission data is sent if the information comprised inthe contention based grant so indicates, e.g. a state bit is detected tobe set to the first value, and retransmission data is sent if theinformation, based on that no collision was detected, is set to indicateretransmission, e.g. a state bit is detected to be set to the secondvalue.

After the user equipment 120, 122 has received a NACK on PHICH, it canaccording to some embodiments be prohibited to use contention basedresources for any data by means of a contention based uplink prohibittimer. This data can be RLC retransmission, or possibly some new data.The prohibit timer can be valid over a fixed time period or until thenext dynamic grant for the user equipment's 120, 122 Cell Radio NetworkTemporary Identifier (C-RNTI). When the optional prohibit timer isrunning, the user equipment 120, 122 may be able to do a schedulingrequest on the Physical Uplink Control Channel (PUCCH).

The specific embodiment comprising the prohibit timer described above isparticularly useful in the case where a collision was detected, but mayalso be applied in case a NACK is received but no collision wasdetected. In the collision scenario, the prohibit timer may for exampleconstitute an alternative to the addition of a random delay beforetransmitting an RLC transmission.

In LTE systems, data unit reordering due to HARQ retransmissions may becorrected by the RLC layer. A reordering timer may be used to wait forpotentially successful retransmissions in case a gap in received RLCsequence numbers is detected according to some embodiments. Thetransmission of a status report to request an RLC retransmission may bedelayed until the timer expires, and cancelled if the retransmission wassuccessful in the mean time. With contention based uplink, thereordering timer may be used if MAC level retransmissions are performedand soft combining is used. Else any gap may be due to loss of data.

According to some embodiments, a local NACK may be passed in the userequipment 120, 122 from the MAC layer to the RLC layer, i.e. the localNACK is given from MAC to RLC in the UE, which triggers an RLCretransmission of the lost data. As no variance in MAC transmissiondelay occurs, the reordering timer in the RLC receiver may not beneeded. The RLC layer may also be made aware whether MAC layerretransmission is supported or not. RLC polling for status reports canalso be optimized, or at least somehow improved, for contention basedtransmissions. The importance of the RLC polling mechanism is reduced ifretransmissions are mostly triggered by local NACKs due to missing MACACK according to some embodiments. Accordingly, the optional poll timermay be reduced to a pure safeguard mechanism to prevent protocol stall,i.e. the value of the timer could be increased or the timer be switchedoff. Polling on empty buffer is then sufficient and could be triggeredby checking the buffer status according to some embodiments.

FIG. 3 a is an illustration depicting an operation with successful radiosignal transmission, according to some embodiments.

Data transmission on contention based grants may be scheduled on PDCCHby sending a contention based grant, addressed to a contentionbased-Radio Network Temporary Identifier CB-RNTI. Which CB-RNTIs eachuser equipment 120, 122 should listen to may be preconfigured with RRC.Once a user equipment 120, 122 has data in its buffer and detects acontention based grant, it may try to transmit its data in thecorresponding uplink resource blocks, using the transport formatindicated in the grant. Once the transmission is made, the userequipment 120, 122 monitors the Physical HARQ Indication Channel (PHICH)for the HARQ feedback of the uplink transmission. In case an ACK isreceived, the user equipment 120, 122 interprets the transmission assuccessful and may continue data transmission in the next contentionbased grant. Note that this description considers only HARQ process 0 inFIG. 3 a. The user equipment 120, 122 may simultaneously performtransmission on the other HARQ processes as well, according to someembodiments.

According to the embodiments illustrated in FIGS. 3 a-c, the basestation 110 controls the HARQ operation by using the NDI field in thecontention based grant for providing information indicating if thecontention based grant should be used for initial transmission orretransmission. Setting the NDI=0 may indicate that user equipment 120,122 may only use the contention based grant for initial transmission,e.g. because a collision was detected. Setting the NDI=1 may indicatethat the grant is only for HARQ retransmissions, i.e. only a userequipment 120, 122 that performed a transmission on the same HARQprocess one Round Trip Time, RTT, before and received a NACK is allowedto use the contention based grant to transmit a HARQ retransmission. Inthis way, a user equipments 120, 122 wanting to initiate newtransmission are blocked from using this contention based grant and thecollision probability is decreased.

Note that the use of 0 and 1 may as well be reversed, such that settingthe NDI=1 may indicate that user equipment 120, 122 may only use thecontention based grant for initial transmission. Setting the NDI=0 mayoptionally indicate that the grant is only for HARQ retransmissions,i.e. only a user equipment 120, 122 that performed a transmission on thesame HARQ process one RTT before and received a NACK is allowed to usethe contention based grant to transmit a HARQ retransmission.

FIG. 3 b is an illustration depicting unsuccessful radio signaltransmission, according to some embodiments, due to collision.

The base station 110 in this specific embodiment uses the NDI bit tocontrol the HARQ operation by enabling HARQ when it does not detect acollision, and to disable HARQ when a collision is detected. If the basestation 110 detects a collision, it may set e.g. the NDI=0 in the nextgrant for the same HARQ process, to indicate to the accessing userequipments in the contention based group that they should not performHARQ retransmission. Instead, the colliding user equipments 120, 122 maygenerate a local NACK to trigger a higher layer (RLC) retransmission. Inaddition, colliding user equipments 120, 122 may according to someembodiments implement a backoff time until accessing contention basedgrant again in order to avoid successive collisions, according to someembodiments.

FIG. 3 c is an illustration depicting unsuccessful radio signaltransmission (a NACK is sent), according to some embodiments, where nocollision is detected.

If the base station 110 does not detect a collision, but the decoding ofthe received data fails, it orders the transmitting user equipment 120,122 to perform a HARQ retransmission by providing a contention basedgrant with NDI=1 according to some embodiments and the same format asthe initial transmission on the same HARQ process, see FIG. 3 c.

In an alternative embodiment of the invention the base station 110controls the HARQ operation by means of selecting different CB-RNTIs forindicating initial transmission and HARQ retransmission, respectively.Providing a contention based uplink grant to a first CB-RNTI indicatesthat user equipments 120, 122 may only use the contention based grantfor initial transmission. Providing a contention based uplink grant to asecond CB-RNTI indicates that the grant is only for HARQretransmissions, i.e. only a user equipments 120, 122 that performed atransmission on the same HARQ process one RTT before and received a NACKis allowed to use the contention based grant to transmit a HARQretransmission.

In this way, user equipments 120, 122 wanting to initiate newtransmission are blocked from using this contention based grant and thecollision probability is decreased.

The base station 110 can use different techniques to determine whetherthere was a collision on a contention based resource. A high receivedenergy, but failed decoding could be interpreted as a collision. A lowreceived energy, and increased noise could instead be interpreted as apower limited user equipment 120, 122, according to some embodiments. Inthe second case, HARQ retransmission may provide enough accumulatedreceived energy to correctly decode the data. Another way to supportcollision detection may be to let user equipments 120, 122 use differentreference symbols in their contention based transmissions. There willnot be enough reference symbols for each user equipment 120, 122, but arandomly selected reference symbol may in some cases allow the basestation 110 to detect a collision according to some embodiments.

A user equipment 120, 122 having data to transmit detects a contentionbased grant and then transmits the data on the contention basedresources indicated in the grant. The user equipment 120, 122 may storethe soft bits in the HARQ process buffer and then reads the HARQfeedback information on the PHICH resource indicated in the contentionbased grant. If the HARQ feedback indicates an ACK, the user equipment120, 122 considers the transmission successful and flushes the HARQprocess buffer. If the HARQ feedback indicates NACK, the user equipment120, 122 reads the contention based grant corresponding to the nextuplink subframe of the same HARQ process and determines what theinformation comprised in the contention based grant indicates, forexample the value of the NDI bit.

If the information comprised in the contention based grant indicatesthat a transmission should not be performed, which for example may beindicated by an NDI set to 0, the user equipment 120, 122 flushes theHARQ process buffer and generates a local NACK to trigger RLCretransmission according to some embodiments. To avoid successivecollisions, a network defined random backoff time, i.e. delay, may beapplied according to some embodiments.

If the information comprised in the contention based grant indicatesthat a retransmission should be made, e.g. NDI bit is set to 1, the userequipment 120, 122 performs a HARQ retransmission in the contentionbased grant according to some embodiments. Note that the base station110 must make sure the contention based grant is of same type as theinitial grant so that the user equipment 120, 122 can perform theretransmission. In case there are several contention based grants in thesame subframe, one way of distinguish the grants from each other is todefine several contention based RNTIs, one for each contention basedgrant. The retransmission is then to be performed on the same CB-RNTI asthe original transmission according to some embodiments.

As previously mentioned, in an alternative embodiment of the inventiondifferent CB-RNTIs are used for indicating initial transmission and HARQretransmission. Receiving an uplink grant for a first CB-RNTI indicatesthat the user equipment 120, 122 may only use the contention based grantfor initial transmission. Receiving an uplink grant for a second CB-RNTIindicates that a user equipment 120, 122 that performed a transmissionon the same HARQ process one RTT before and received a NACK can use thecontention based grant to transmit a HARQ retransmission.

FIG. 4 is a flow chart illustrating embodiments of method steps 401-407performed in a base station 110 for scheduling user equipments 120, 122in a cell 130. The base station 110 and the user equipments 120, 122 arecomprised in a wireless communication system 100. The wirelesscommunication system 100 is adapted for contention based transmissions.The base station 110 is adapted to schedule communication from the userequipments 120, 122 by sending contention based grants. Each contentionbased grant comprises information indicating if the contention basedgrant should be used for initial transmission or for retransmission. Theinformation may be e.g. a state bit, which state bits are adapted to beset to a first value or to a second value. The state bit may be e.g. aNew Data Indicator NDI. Alternatively, the information may, as describedabove, be comprised in the selection of CB-RNTI. The base station 110 isadapted to serve a plurality of user equipments 120, 122 within the cell130. The wireless communication system 100 may be e.g. a LTE radionetwork and the base station 110 may be e.g. an evolved node B, eNB,according to some embodiments.

Thus, if a collision is detected, the following contention based grantcomprises information set to indicate that the contention based grant isto be used for initial transmission. Otherwise, if data is not correctlyreceived, but no collision is detected, the information in thecontention based grant is set to indicate that the contention basedgrant is to be used for retransmission, such as e.g. a Hybrid AutomaticRepeat Request HARQ retransmission.

To appropriately scheduling user equipments 120, 122 within the cell130, the method may comprise a number of method steps 401-407.

It is however to be noted that some of the described method steps areoptional and only comprised within some embodiments. Further, it is tobe noted that the method steps 401-407 may be performed in a somewhatdifferent chronological order and that some of them, e.g. step 404 andstep 405, may be performed simultaneously or in an altered chronologicalorder. The method may comprise the following steps:

Step 401

A contention based grant is sent to a plurality of user equipments 120,122 within the cell 130.

The plurality of user equipments 120, 122 within the cell 130 mayoptionally comprise a subset of all the user equipments 120, 122 withinthe cell 130. For example, some user equipments 120 may be comprised ina premium contention based group and some user equipments 122 may becomprised in a regular contention based group.

According to some embodiments, the plurality of user equipments 120, 122within the cell 130 may optionally comprise all the user equipments 120,122 within the cell 130.

The feedback ACK/NACK may according to some embodiments be sent over aPhysical Hybrid Automatic Repeat Request Indicator Channel (PHICH).

Step 402

Data is received from at least one user equipment 120, 122.

Step 403

It is verified if data is correctly received from at least one userequipment 120, 122.

The data verification may comprise decoding, or attempting to decode thedata and perform e.g. a cyclic redundancy check CRC, or any otherappropriate data verification procedure.

Step 404

If it is verified that data is not correctly received anon-acknowledgement feedback NACK is sent to the plurality of userequipments 120, 122.

Step 405

If it is verified that data is not correctly received, it is detected ifdata is not correctly received due to a collision. If it is detectedthat data is not correctly received due to a collision, information isprovided with the following contention based grant to indicate that saidcontention based grant should be used for initial transmission. Theinformation may be provided as a state bit in the second, i.e. followingcontention based grant set to a first value, indicating that the saidcontention based grant is only to be used for initial transmission.Alternatively, the information is provided to the user equipments by theselection of a CB-RNTI used for the following contention based grant,indicating that said contention based grant is only to be used forinitial transmission.

However, if data is not correctly received, but no collision isdetected, the information in the following contention based grant is setto indicate that said contention based grant is only to be used forretransmission, such as e.g. a HARQ retransmission, e.g. a state bit inthe second, i.e. following contention based grant is set to the secondvalue, or a CB-RNTI is selected, to indicate that said contention basedgrant is only to be used for retransmission.

Step 406

A second, i.e. following contention based grant, belonging to the sameretransmission process as the first contention based grant, is sent tothe plurality of user equipments 120, 122 to be used in accordance withthe information indicating if the contention based grant should be usedfor initial transmission or retransmission.

Step 407

If it is verified that data is correctly received, an acknowledgementfeedback ACK may be sent to the plurality of user equipments 120, 122.

FIG. 5 schematically illustrates an arrangement 500 in a base station110. The arrangement 500 is adapted to perform the method steps 401-407in order to schedule user equipments 120, 122 in a cell 130. The basestation 110 and the user equipments 120, 122 are comprised in a wirelesscommunication system 100. The wireless communication system 100, thebase station 110 and the user equipments 120, 122 are adapted forcontention based transmissions. The base station 110 is adapted toschedule the communication from the user equipments 120, 122 by sendingcontention based grants. Each contention based grant comprisesinformation indicating if the contention based grant should be used forinitial transmission or for retransmission. The base station 110 isadapted to serve a plurality of user equipments 120, 122 within the cell130. The wireless communication system 100 may be e.g. a LTE radionetwork and the base station 110 may be e.g. an evolved node B, eNB,according to some embodiments.

In order to perform the method steps 401-407 correctly, the base stationarrangement 500 comprises e.g. a transmitter 510, adapted to send acontention based grant, and to send transmission feedback to a pluralityof user equipments 120, 122 within the cell 130. The transmissionfeedback may be an ACK or a NACK. Also, the arrangement 500 comprises areceiver 520. The receiver 520 is adapted to receive data from at leastone user equipment 120, 122. In addition, the arrangement 400 comprisesa verification unit 530, adapted to verify if the data is correctlyreceived from at least one user equipment 120, 122. Additionally, thearrangement 500 comprises a detecting unit 540, adapted to detect ifdata is not correctly received due to a collision. Furthermore, thearrangement 500 comprises a determination unit 550, adapted to generatefeedback and set information to be associated with each contention basedgrant, by setting a status bit or by selection of CB-RNTI to indicate ifthe contention based grant is to be used for initial transmission orretransmission.

The arrangement 500 may also comprise a feedback unit. The feedback unitmay be adapted to generate acknowledgement feedback ACK if it isverified that data has been correctly received from at least one userequipment 120, 122. The feedback unit may further be adapted to generatenon-acknowledgement feedback NACK if no data is correctly received fromany user equipment 120, 122.

The arrangement 500 may further comprise a processing unit 560 which maybe represented by e.g. a Central Processing Unit (CPU), a processor, amicroprocessor, or other processing logic that may interpret and executeinstructions. The processing unit 560 may perform data processingfunctions for inputting, outputting, and processing of data includingdata buffering and device control functions, such as call processingcontrol, user interface control, or the like.

It is to be noted that any internal electronics of the base station 110and/or the base station arrangement 500, not completely necessary forunderstanding the present method according to the method steps 401-407has been omitted from FIG. 5, for clarity reasons. Further, it is to benoted that some of the described units 510-560 comprised within thearrangement 500 in the base station 110 are to be regarded as separatelogical entities but not with necessity separate physical entities. Tomention an example, the receiving unit 520 and the transmitting unit 510may be comprised or co-arranged within the same physical unit, atransceiver, which may comprise a transmitter circuit and a receivercircuit, which transmits outgoing radio frequency signals and receivesincoming radio frequency signals, respectively, via an antenna. Theradio frequency signals transmitted between the base station 110 and theuser equipments 120, 122 may comprise both traffic and control signalse.g. paging signals/messages for incoming calls, which may be used toestablish and maintain a voice call communication with another party orto transmit and/or receive data, such as SMS, e-mail or MMS messages,with a remote user equipment.

The method steps 401-407 in the base station 110 may be implementedthrough one or more processor units 560 in the base station 110,together with computer program code for performing the functions of thepresent method steps 401-407. Thus a computer program product,comprising instructions for performing the method steps 401-407 in thebase station 110 may schedule user equipments 120, 122 in a cell 130.

The computer program product mentioned above may be provided forinstance in the form of a data carrier carrying computer program codefor performing the method steps according to the present solution whenbeing loaded into the processor unit 560. The data carrier may be e.g. ahard disk, a CD ROM disc, a memory stick, an optical storage device, amagnetic storage device or any other appropriate medium such as a diskor tape that can hold machine readable data. The computer program codecan furthermore be provided as program code on a server and downloadedto the base station 110 remotely, e.g. over an Internet or an intranetconnection.

Further, a computer program product comprising instructions forperforming at least some of the method steps 401-407 may be used forimplementing the previously described method in the base station 110 forproviding feedback to user equipments 120, 122 in a cell 130, when thecomputer program product is run on a processing unit 560 comprisedwithin the base station 110.

FIG. 6 is a flow chart illustrating embodiments of method steps 601-609performed in a user equipment 120 for assisting a base station 110 inscheduling user equipments 120, 122 in a cell 130. The base station 110and the user equipments 120, 122 are comprised in a wirelesscommunication system 100. The wireless communication system 100, thebase station 110 and the user equipments 120, 122 are adapted forcontention based transmissions. The base station 110 is adapted toschedule the communication from the user equipments 120, 122 by sendingcontention based grants. A contention based grant comprises informationindicating if the contention based grant should be used for initialtransmission or for retransmission. The wireless communication system100 may be e.g. a LTE radio network and the base station 110 may be e.g.an evolved node B, eNB, according to some embodiments. The userequipment 120 may be restricted to use the received contention basedgrant only for transmitting data for the first time within a process,i.e. initial transmission, if the information comprised thereinindicates that the contention based grant is to be used for initialtransmission.

To appropriately send data packets and receive ACK/NACK and contentionbased grants from the base station 110 concerning the reception statusof the sent data packets, the method may comprise a number of methodsteps 601-609.

It is to be noted that the method steps 601-609 may be performed in asomewhat different chronological order and that some of them, e.g. step604 and step 605, may be performed simultaneously or in an alteredchronological order. Further, it is to be noted that some method stepse.g. step 604, 605, 606, 607, 608 and step 609 are optional and may onlybe performed within some embodiments. The method may comprise thefollowing steps:

Step 601

A contention based grant comprising information indicating if the grantshould be used for initial transmission or for retransmission isreceived from the base station 110.

Step 602

It is detected whether the grant should be used for initial transmissionor for retransmission, for example if a state bit comprised in thereceived contention based grant is set to the first value or to thesecond value.

Step 603

Data is sent to the base station 110. The data is sent according to theinformation provided with the received contention based grant, such thatdata to be sent to the base station 110 is initial transmission data iffor example a state bit is detected to be set to the first value, andretransmission data if the state bit is detected to be set to the secondvalue.

Step 604

An acknowledgement feedback ACK or non-acknowledgement feedback NACKfrom the base station 110 may be received.

Step 605

This step is optional and may only be performed within some embodiments.

New data to be sent to the base station 110 may be prepared, when nextcontention based grant of the same retransmission process as the firstgrant is received, if the information provided with the followingcontention based grant, e.g. a state bit, is detected to indicate thatthe contention based grant should be used for initial transmissionaccording to some embodiments.

Step 606

This step is optional and may only be performed within some embodiments.

A radio link control retransmission may be triggered if a NACK isreceived and the information provided with the following contentionbased grant of the same retransmission process as the first grant isdetected to indicate that said grant should be used for initialtransmission according to some embodiments.

Step 607

According to some embodiments, a random delay may be added before theradio link control, RLC, retransmission of data is performed in order tospread the RLC retransmission in time.

Step 608

A retransmission of data, such as e.g. a HARQ retransmission may beperformed if a NACK is received and the next contention based grant ofthe same retransmission process as the received grant comprisesinformation that is detected to indicate that the contention based grantshould be used for re-transmission, e.g. a state bit is set to a secondvalue.

Step 609

This step is optional and may only be performed within some embodiments.

If a NACK is received, a sending prohibit timer 790 may be activated forthe purpose of load controlling, which sending prohibit timer 790prevents the user equipment 120 from using any contention based grantsreceived from the base station 110 before the sending prohibit timer 790has timed out.

This optional step may be performed regardless of whether the NACK wascaused by a collision, see step 606, whereby an RLC retransmission isperformed, or if a collision did not occur, see step 608, whereby a HARQretransmission is performed.

The optional sending prohibit timer 790 may be arranged to bedeactivated when a dynamic grant, dedicated to the user equipment 120,is received, according to some embodiments.

In a specific embodiment, the sending prohibit timer may be set to zero.

FIG. 7 schematically illustrates an arrangement 700 in a in a userequipment 120. The arrangement 700 is adapted to perform the methodsteps 601-609. Thus the user equipment arrangement 700 is adapted toreceive feedback from a base station 110 concerning the reception statusof data sent to the base station 110, and contention based grants. Thebase station 110 and the user equipment 120 are comprised in a wirelesscommunication system 100 adapted for contention based transmissions. Thebase station 110 is adapted to schedule communication from the userequipments 120, 122 by sending contention based grants. Each contentionbased grant comprises information indicating if the contention basedgrant should be used for initial transmission or retransmission. Theinformation may according to some embodiments be a state bit, whichstate bit is adapted to be set to a first value or to a second value.Alternatively, the information may be transferred by selection ofdifferent CB-RNTI:s dependent on if the contention based grant should beused for initial transmission or retransmission. The base station 110 isadapted to serve a plurality of user equipments 120, 122 within a cell130. The user equipment 120 may be a mobile terminal such as e.g. amobile phone. The wireless communication system 100 may be e.g. a LTEradio network.

In order to perform the method steps 601-609, the arrangement 700comprises units such as e.g. a receiver 710, adapted to receive acontention based grant comprising information indicating if thecontention based grant should be used for initial transmission orretransmission, and also acknowledgement feedback ACK ornon-acknowledgement feedback NACK from the base station 110.Additionally, the arrangement 600 comprises a detecting unit 720,adapted to detect if the information comprised in the receivedcontention based grant is set to indicate if the contention based grantshould be used for initial transmission or retransmission, for exampleif a state bit is set to a first value or to a second value. Also, thearrangement 700 comprises a transmitter, adapted to send data to thebase station 110.

The arrangement 700 may further comprise a processing unit 780, whichmay be represented by e.g. a Central Processing Unit (CPU), a processor,a microprocessor, or other processing logic that may interpret andexecute instructions. The processing unit 780 may perform dataprocessing functions for inputting, outputting, and processing of dataincluding data buffering and device control functions, such as callprocessing control, user interface control, or the like.

Furthermore, according to some embodiments, the arrangement 700 may alsocomprise a sending prohibit timer 790. The optional sending prohibittimer 790 may be adapted to prohibit the user equipment 120 from usingany received contention based grant within a certain time. According tosome embodiments, the sending prohibit timer 790 becomes activated whenthe user equipment 120 receives a NACK from the base station 110. Whenactivated, the sending prohibit timer 790 may prohibit the userequipment 120 from using any contention based resources i.e. contentionbased grants for sending any data. The sending prohibit timer 790 may bevalid over a fixed, predetermined period of time, or it may be activeuntil the next dynamic grant for the user equipment 120 is received.When the sending prohibit timer 790 is running, the user equipment 120may be able to do a scheduling request on the Physical Uplink ControlCHannel (PUCCH). The scheduling request may be used by the userequipment 120 to request allocation of uplink resources when having dataready for transmission, but no resource grant for use of the PhysicalUplink Shared CHannel (PUSCH).

Additionally, the user equipment 120 may comprise a buffer or anothermemory for storing data for transmission. The data can for example bereceived from an application executed in the user equipment 120. Acontroller which may be implemented in the processor 780, may selecte.g. a resource block responsive to the status of the buffer, e.g. whendata for transmission is detected, and the allocation determined by theprocessor 780, i.e. when it is detected that the resource block can beused by a plurality of user equipments 120, 122 comprising the presentuser equipment 120. The data may then be forwarded to the transmitter720, e.g. using a physical layer of the user equipment 120, and at leasta first part of the data may be transmitted using the resource blockselected by the controller.

It is to be noted that any internal electronics of the user equipment120 and/or the user equipment arrangement 700, not completely necessaryfor understanding the present method according to the method steps601-609 has been omitted from FIG. 7, for clarity reasons. Further, itis to be noted that some of the described units 710-790 comprised withinthe arrangement 700 in the user equipment 120 are to be regarded asseparate logical entities but not with necessity separate physicalentities. To mention an example, the receiver 710 and the transmitter720 may be comprised or co-arranged within the same physical unit, atransceiver, which may comprise a transmitter circuit and a receivercircuit, which transmits outgoing radio frequency signals and receivesincoming radio frequency signals, respectively, via an antenna. Theradio frequency signals transmitted between the base station 110 and theuser equipments 120, 122 may comprise both traffic and control signalse.g. paging signals/messages for incoming calls, which may be used toestablish and maintain a voice call communication with another party orto transmit and/or receive data, such as SMS, e-mail or MMS messages,with a remote user equipment.

The mechanism for sending and/or receiving data packets andsending/receiving ACK/NACK acknowledgements and contention based grantsmay be implemented through one or more processors 780 in the userequipment arrangement 700 depicted in FIG. 7, together with computerprogram code for performing the method steps 601-609 of the presentsolution. The program code mentioned above may also be provided as acomputer program product, for instance in the form of a data carriercarrying computer program code for performing the present solution whenbeing loaded into the user equipment 120. One such carrier may be in theform of a memory stick. It is however feasible with other data carriers.The computer program code may furthermore be provided as program code ona server and downloaded to the user equipment 120 remotely.

When using the formulation “comprise” or “comprising” it is to beinterpreted as non-limiting, i.e. meaning “consist at least of”. Thepresent invention is not limited to the above described preferredembodiments. Various alternatives, modifications and equivalents may beused.

1-17. (canceled)
 18. A method in a base station for scheduling userequipments, the method comprising: sending a contention based grant of aretransmission process to a set of user equipments within a cell servedby the base station; receiving data from at least one of the set of userequipments using the contention based grant; determining whether thedata is correctly received from the at least one user equipment; andresponsive to determining that the data is not correctly received, themethod further comprising the steps: sending a non-acknowledgementfeedback to the set of user equipments; detecting whether the data wasnot correctly received due to a collision; and sending a followingcontention based grant to the set of user equipments, wherein thefollowing contention based grant comprises information, based on thedetecting step, indicating whether the following contention based grantshould be used for initial transmission or for retransmission.
 19. Themethod according to claim 18, wherein the information indicates that thefollowing contention based grant is to be used for initial transmissionin response to detecting that the data was not correctly received due tothe collision.
 20. The method according to claim 18, wherein theinformation indicates that the following contention based grant is to beused for retransmission if the data was not correctly received in anabsence of collision.
 21. The method according to claim 18, wherein theinformation indicating whether the following contention based grantshould be used for initial transmission or for retransmission isprovided as one of an identifier used to address the user equipments anda state bit indicator; wherein a first value of the state bit indicatorindicates that the following contention based grant should be used forinitial transmission and a second value of the state bit indicatorindicates that the following contention based grant should be used forretransmission.
 22. The method according to claim 21, wherein the statebit indicator is a New Data Indicator.
 23. The method according to claim21, wherein the identifier used to address the user equipments is aContention Based-Radio Network Temporary Identifier “CB-RNTI”, andwherein different CB-RNTIs are used for indicating if the followingcontention based grant should be used for initial transmission or forretransmission.
 24. A base station for scheduling user equipments in acell, the base station comprising: a transmitter that sends contentionbased grants and feedback to a set of user equipments within the cellserved by the base station; a receiver that receives data from at leastone of the set of user equipments; a verification unit that determineswhether the data is correctly received from the at least one of the setof user equipments; a detecting unit that detects whether the data wasnot correctly received due to a collision; a determination unit thatgenerates feedback, and wherein the determination unit further setsinformation comprised in a following contention based grant whichindicates whether the following contention based grant should be usedfor initial transmission or for retransmission, wherein: responsive todetermining that the data is not correctly received and the collision isdetected, the information in the following contention based grant is setto indicate that the following contention based grant is to be used forinitial transmission; and responsive to determining that the data is notcorrectly received in an absence of collision, the information in thefollowing contention based grant is set to indicate that the followingcontention based grant is to be used for retransmission.
 25. A method ina user equipment for assisting in scheduling of user equipments in acell served by a base station, the method comprising: receiving acontention based grant from the base station, wherein the contentionbased grant comprises information indicating whether the contentionbased grant should be used for initial transmission or retransmission,wherein the information is an identifier used to address the userequipment; detecting the information comprised in the contention basedgrant, and sending data to the base station using said contention basedgrant, according to the identifier used to address the user equipment.26. The method according to claim 25, wherein the identifier used toaddress the user equipment is a Contention Based-Radio Network TemporaryIdentifier “CB-RNTI”, and wherein different CB-RNTIs are used forindicating if the contention based grant should be used for initialtransmission or for retransmission.
 27. The method according to claim25, further comprising: if a non-acknowledgement feedback is receivedand the information comprised in the following grant of the sameretransmission process as the first grant indicates that the grantshould be used for initial transmission, triggering a radio link controlretransmission.
 28. The method according to claim 25, furthercomprising: if a non-acknowledgement feedback is received and theinformation comprised in the following grant of the same retransmissionprocess as the first grant indicates that the grant should be used forretransmission, performing a retransmission of the data with a HybridAutomatic Repeat Request retransmission.
 29. The method according toclaim 27, further comprising at least one of: adding a random delaybefore the radio link control retransmission of data is performed andactivating a sending prohibit timer, which sending prohibit timerprevents the user equipment from using any contention based grantsreceived from the base station before the sending prohibit timer hastimed out.
 30. The method according to claim 29, wherein the sendingprohibit timer is arranged to be deactivated when a dynamic grant,dedicated to the user equipment, is received.
 31. User equipment forassisting in scheduling of user equipments in a cell served by a basestation, the user equipment comprising: a receiver, adapted to receive acontention based grant comprising information indicating whether thecontention based grant should be used for initial transmission or forretransmission, wherein the information is an identifier used to addressthe user equipment; a detecting unit, adapted to detect saidinformation, and a transmitter, adapted to transmit data to the basestation using said contention based grant, according to the identifierused to address the user equipment.
 32. The user equipment of claim 31,wherein the identifier used to address the user equipment is a set ofCB-RNTIs, wherein different CB-RNTIs are used for indicating if afollowing contention based grant should be used for initial transmissionor for retransmission.
 33. The user equipment of claim 31, furtheradapted to trigger a radio link control retransmission if anon-acknowledgement feedback is received and the information comprisedin the following grant of the same retransmission process as the firstgrant indicates that the grant should be used for initial transmission.34. The user equipment of claim 31, further adapted to perform aretransmission of the data with a Hybrid Automatic Repeat Requestretransmission if a non-acknowledgement feedback is received and theinformation comprised in the following grant of the same retransmissionprocess as the first grant indicates that the grant should be used forretransmission.
 35. The user equipment of claim 33, further adapted toadd a random delay before the radio link control retransmission of datais performed.
 36. The user equipment of claim 33, further adapted toactivate a sending prohibit timer, which sending prohibit timer preventsthe user equipment from using any contention based grants received fromthe base station before the sending prohibit timer has timed out. 37.The user equipment of claim 36, further adapted to deactivate thesending prohibit timer when a dynamic grant, dedicated to the userequipment, is received.